ReorderList - bind to DataTable; save changes

Introduction

The ReorderList is one of the coolest controls in the ASP.NET AJAX Control Toolkit. This article intends to give a basic outline of how to subclass the control so you can bind it to a DataTable and, on a Reorder event, save the new order to the database. There is no source code to download with this article, only code sighted within. The focus of this article is on the ReorderList and not on saving and retrieving data from a database.

The Problem

The ReorderList expects as it's DataSource, an object that implements IList. My business objects work mostly with DataSets and DataTables and I wanted to bind to a DataTable. The control will load data from a DataTable but on a Reorder event an exception will be thrown stating the DataTable does not implement IList. I tried using ((IListSource)DataTable).GetList() but that didn't go anywhere.

The Solution

To begin, create a subclass of the ReorderList and override the DoReorder method like this:

using System;
using System.Data;
using AjaxControlToolkit;

namespace My.Web.UI.Controls
{
    public class myReorderList : ReorderList
    {
        protected override bool DoReorder(int oldIndex, int newIndex)
        {
            if (DataSource is DataTable)
            {
                DataRowCollection rows = ((DataTable)DataSource).Rows;
                int NewListOrder = (int)rows[newIndex][SortOrderField];

                if (oldIndex < newIndex) //item moved down
                {
                    for (int i = oldIndex + 1; i <= newIndex; i++)
                    {
                        rows[i][SortOrderField] = 
                    (int)rows[i][SortOrderField] - 1;
                    }
                }
                else  //item moved up
                {
                    for (int i = oldIndex - 1; i >= newIndex; i--)
                    {
                        rows[i][SortOrderField] = 
                    (int)rows[i][SortOrderField] + 1;
                    }
                }
                rows[oldIndex][SortOrderField] = NewListOrder;
                return true;
            }
            else
            {
                throw new InvalidOperationException
            ("DataSource is not a System.Data.DataTable.");
            }
            return false;
        }
    }
}

Here is some example code for an aspx page that is almost exactly like the code found in ReorderList.aspx in the Samples project of the ASP.NET AJAX Control Toolkit. The one exception is the addition of OnItemReorder="ReorderList1_ItemReorder". Also notice SortOrderField="Priority". This indicates the name of the column in the data source DataTable that stores the item's order in the group. This property is used in the overridden DoReorder method in the subclass (sighted above) to store the new order. The subclassed control expects this column to be an int column.

<MyAjaxToolkit:myReorderList ID="ReorderList1" runat="server"
    PostBackOnReorder="false"
    CallbackCssStyle="callbackStyle"
    DragHandleAlignment="Left"
    ItemInsertLocation="End"
    DataKeyField="ItemID"
    SortOrderField="Priority"
    OnItemReorder="ReorderList1_ItemReorder">
    <ItemTemplate>
        <div class="itemArea">
            <asp:Label ID="Label1" runat="server"
                Text='<%# HttpUtility.HtmlEncode(Convert.ToString(Eval("Title"))) %>' />
            <asp:Label ID="Label2" runat="server"
                Text='<%# HttpUtility.HtmlEncode(Convert.ToString(Eval("Description", " - {0}"))) %>' />
        </div>
    </ItemTemplate>
    <EditItemTemplate>
        <div class="itemArea">
            <asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("Title") %>' />
            <asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("Description") %>' />
            <asp:TextBox ID="TextBox4" runat="server" Text='<%# Bind("Priority") %>' />
        </div>
    </EditItemTemplate>
    <ReorderTemplate>
        <asp:Panel ID="Panel2" runat="server" CssClass="reorderCue" />
    </ReorderTemplate>
    <DragHandleTemplate>
        <div class="dragHandle"></div>
    </DragHandleTemplate>
    <InsertItemTemplate>
        <!-- bottom border is workaround for IE7 Beta issue where bg doesn't render -->
        <div style="padding-left:25px; border-bottom:thin solid transparent;">
            <asp:Panel ID="panel1" runat="server" DefaultButton="Button1">
                <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("Title") %>' />
                <asp:Button ID="Button1" runat="server" CommandName="Insert" Text="Add" />
                <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"
                    ErrorMessage="Please enter some text" ControlToValidate="TextBox1" />
            </asp:Panel>
        </div>
    </InsertItemTemplate>
</MyAjaxToolkit:myReorderList>

Then in the code behind the aspx page, we need something like this:

protected void Page_Load(object sender, EventArgs e)
{
    ReorderList1.ItemDataBound += 
    new EventHandler<AjaxControlToolkit.ReorderListItemEventArgs>
                    (ReorderList1_ItemDataBound);
    if (!IsPostBack)
    {
        BindReorderList();
    }
    else
    {
        // Need code here to retrieve the data source DataTable from
        // the Session object or other persistence method and assign it to
        // ReorderList1.DataSource property
    }
}

void BindReorderList()
{
    // Need code here to fill SomeDataTable with a DataTable.
    // It must contain an int column named in the SortOrderField
    // property of the myReorderList control markup in the aspx page

    ReorderList1.DataSource = SomeDataTable;
    ReorderList1.DataBind();

    //Need to save SomeDataTable to the Session object or 
    //other persistence method
}

protected void ReorderList1_ItemReorder(object sender, 
        AjaxControlToolkit.ReorderListItemReorderEventArgs e)
{
    // need code to save changes made to the data source DataTable
    // The changes were made in the overridden DoReorder method
    // in the MyReorderList control

    BindReorderList();
}

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